Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $224.95   12.347%   $252.7246   $252.72   $252.70   $252.70  
  Purchase #2 $33.39   4.260%   $34.8124   $34.81   $34.80   $34.80  
  Purchase #3 $90.57   9.153%   $98.8599   $98.86   $98.85   $98.90  
  Purchase #4 $59.99   5.497%   $63.2877   $63.29   $63.30   $63.30  
  Purchase #5 $76.31   10.770%   $84.5286   $84.53   $84.55   $84.50  
  Purchase #6 $229.75   10.317%   $253.4533   $253.45   $253.45   $253.50  
  Purchase #7 $217.62   4.274%   $226.9211   $226.92   $226.90   $226.90  
  7 purchase totals = $932.58       $1,014.5876   $1,014.58   $1,014.55   $1,014.60